Surface analysis of zinc oxide, silica-supported silver and platinum model catalysts under various conditions
Date
2020
Authors
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Publisher
University of Delaware
Abstract
There have been tremendous efforts in last one decade to investigate molecular level interfacial chemistry of heterogenous processes under realistic conditions. Several model catalysts have been studied with the help of state-of-the-art in-situ spectroscopic and imaging capabilities offered by modern surface science. In this dissertation the synthesis and quantitative analysis of heterogeneous systems will be explored by a variety of surface science techniques to elucidate complex electronic and chemical properties of these surfaces under ambient condition. ☐ In particular, Chapter 1 of this dissertation gives a general overview of the basic principle, importance and applications of x-ray photoelectron spectroscopy (XPS), ambient pressure XPS, and various techniques of metal deposition on selected supports. Specifically, the second chapter will focus on the impact of hydroxylation and adsorption of water on interfacial chemistry of zinc oxide surface. One of the most extensively studied catalyst system of zinc oxide is investigated as a function of relative humidity with high pressure photoelectron spectroscopy. Synchrotron-based ambient pressure photoelectron spectroscopy is utilized and advanced quantification of isobars water uptake are combined with thermodynamic models to compare zinc oxide with previously studied metal oxide systems under similar conditions. These findings based on experimental and theoretical observations suggest that various mechanisms of water dissociation may exist on water/ZnO interface but also that the presence of molecular water and surface carbonates at higher pressures significantly alter the reaction mechanism, promoting further hydroxylation events. ☐ Lastly, two target metals, silver and platinum will be investigated for the effective deposition by metalorganic vapor deposition and wet chemistry techniques, respectively. Last two chapters focus on the deposition of silver and platinum on modified supports using organometallic precursors and reaction mechanism will be investigated using spectroscopy, imaging and computational methods. In case of silver deposition, it is determined that a controlled surface morphology can be obtained by changing the reaction parameters, such as pressure, dosing time, and temperature. In chapter 4, it is observed that the choice of support and reaction conditions significantly affect the final morphology of the platinum nanostructures on the surface. Overall, this dissertation seeks to understand molecular level interfacial chemistry of some of the less understood complex heterogeneous systems with the help of surface sensitive techniques.
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Keywords
APXPS, Deposition, Platinum Precursor, Silver Precursor, Surface Analysis, Zinc Oxide